LM5010 datasheet(11/24 Pages) TI1

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Threshold

IPK

IOCL

Load Current

Increases

Normal Operation

Current Limited

LM5010

www.ti.com

SNVS307F – SEPTEMBER 2004 – REVISED FEBRUARY 2013

Figure 12. Inductor Current - Current Limit Operation

The current limit threshold can be increased by connecting an external resistor (RCL) between SGND and ISEN. The

external resistor typically is less than 1

Ω, and its calculation is explained in the Applications Information section.

The peak current out of SW and ISEN must not exceed 3.5A. The average current out of SW must be less than

3A, and the average current out of ISEN must be less than 2A.

N-Channel Buck Switch and Driver

The LM5010 integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak

current through the buck switch must not be allowed to exceed 3.5A, and the average current must be less than

3A. The gate driver circuit is powered by the external bootstrap capacitor between BST and SW (C4). During

each off-time, the SW pin is at approximately -1V, and C4 is re-charged from VCC through the internal high

voltage diode. The minimum off-time of 265 ns ensures a minimum time each cycle to recharge the bootstrap

capacitor. A 0.022 µF ceramic capacitor is recommended for C4.

Soft Start

The soft start feature allows the converter to gradually reach a steady state operating point, thereby reducing

startup stresses and current surges. Upon turn-on, after VCC reaches the under-voltage threshold (t1 in Figure 8),

an internal 11.5 µA current source charges the external capacitor at the Softstart pin to 2.5V (t2 in Figure 8). The

ramping voltage at SS (and at the non-inverting input of the regulation comparator) ramps up the output voltage

in a controlled manner. This feature keeps the load current from going to current limit during startup, thereby

reducing inrush currents.

An internal switch grounds the Softstart pin if VCC is below the under-voltage lockout threshold, if a thermal

shutdown occurs, or if the circuit is shutdown using the RON/SD pin.

Thermal Shutdown

The LM5010 should be operated so the junction temperature does not exceed 125°C. If the junction temperature

increases above that, an internal Thermal Shutdown circuit activates (typically) at 175°C, taking the controller to

a low power reset state by disabling the buck switch and the on-timer, and grounding the Softstart pin. This

feature helps prevent catastrophic failures from accidental device overheating. When the junction temperature

reduces below 155°C (typical hysteresis = 20°C), the Softstart pin is released and normal operation resumes.

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